A. Field of the Invention
This invention relates to an apparatus and method for detecting labels and more particularly to an apparatus and method for detecting labels removably adhered in a strip-like fashion on a substrate, combining mechanical and proximity sensing. The movement of a mechanical sensor detects the leading edge of the label while a lever arm amplifies that movement for detection by a proximity sensor, thereby providing a label detecting method and apparatus functioning accurately regardless of wear on the mechanical system.
B. Prior Art
It is known in the art of labeling and labeling machines to provide a label detector. A label detector is required and usually incorporated into a labeling device to sense the leading edge of a label on the label's backing material for synchronizing the labeling machine to properly register the label for application to the product. Four types of label detectors are generally known in the art of labeling: optical thru-beam, optical reflective, capacitive, and mechanical.
First, it is known to use a labeling machine employing an optical thru-beam for label detection. The optical thru-beam label detecting device employs a light beam from a source positioned above the label and a receiver positioned below the label backing paper stock. The optical thru-beam detector senses the label by analyzing the differences in light intensities between the backing material opacity and the label with backing material opacity. The main disadvantage of an optical thru-beam label detector is its inability to detect clear or translucent labels because the difference in light intensity between the backing material opacity and the label with backing material opacity is negligible and difficult to analyze.
Second, it is also known to use a labeling machine employing an optical reflective technique to detect labels. The optical reflective technique for detecting labels uses a light source and a receiver positioned above the label at an incident angle. This type of device detects the label by sensing the difference in reflective properties between the backing paper and the label. An optical reflective detector employing this technique, however, requires extremely precise positioning and often produces "false triggers" on different printed regions of the label being detected.
A third method for detecting labels known in the art is described in Herbst, Jr. U.S. Pat. No. 5,650,730 (hereinafter "'730 Patent"). The '730 Patent discloses a label detector using a capacitive technique. The capacitive label detector described in the '730 Patent detects a label by calculating the difference in the dielectric measurement between the backing material without the label and the backing material with the label. It is apparent to those skilled in the art, however, that the capacitive label detector is deficient because it cannot detect labels containing conductive material, such as foil labels. Additionally, this type of label detector is not preferred because it cannot detect labels using conductive inks, particularly carbon based black ink, an ink very common on labels.
Finally, it is known to provide a mechanical label detector using a mechanical switch to sense the difference in thickness between the backing material without the label and the backing material with the label. The thickness differential can be as small as 0.004 inches and still be detected. Mechanical label detectors generally use a high precision mechanical switch mounted to a pin or bearing, which rides over the label material. The switch must be adjusted to open and close exactly where the small motion occurs. In other words, the mechanical label detector has a small finite switching margin. The drawback to the conventional mechanical label detector, however, is the mechanical label detector requires extremely precise adjustment due to the small finite switching margin reflected in the thickness differential. These kinds of adjustments often are difficult to perform. Another drawback to the conventional mechanical label detector is that the detector is frequently thrown out of adjustment from any wear in the system requiring frequent tinkering and replacement of parts.